Video camera tube#Vidicon

A vidicon is a (not to be confused with the picture tube for reproducing a ( TV ) image engl. video camera tube, ) in 1950, developed by RCA image pickup tube. Today, electron tubes are still used by Vidicontyp for special tasks such as in strong bright environment (nuclear power plants ).

History and comparison to other image sensors

Compared to other image pickup tube (about orthicon or Iconoscope ) operating with photocathode and a fast electrical scanning, the vidicon uses a photosensitive layer, which is scanned with a low velocity electron beam. The vidicon was so small at its inception, lighter and more energy efficient, and sat down so rapidly at first in portable cameras through. While the first vidicon worked at RCA with selenium as a photosensitive layer was rapidly transferred to antimony trisulfide because of durability problems. Tubes of Vidicontyps with other semiconductor layers as antimony trisulfide are traded under a different name ( Plumbicon, Saticon, Parsecon, ...).

Operation

The photosensitive layer is composed of semi-conductive Materialialien such as selenium, arsenic, tellurium, and antimony sulfide ( Sb2S3 ). It is applied to a glass sheet that is located on the end wall of the electron tube ( in the above two images, respectively, left). For electrical contact, a transparent, electrically conductive layer, for example of indium tin oxide provides. This signal plate is negatively charged by a electron beam. The image to altered by the different local brightness pointwise the electrical resistance, so that the charges are moving at different speeds to the positive signal plate. There a charge image, which is also read out at each new scan and deleted.

The electron beam is generated with a beam system, such as in a cathode ray tube. The cathode is indirectly heated electrically and is made of appropriate materials in order to release low-temperature electrons. Of the electron beam generator is usually constructed as a triode: through the hole of the negatively charged Wehneltzylinders "picks " the positive field of the acceleration grid, and draws the electron from a viewed by electron microscopy "virtual" cathode ( the virtual cathode is actually a cloud of electrons on the cathode). With the tension of the Wehnelt electrode, the cathode current is controlled. It is a so-called "crossover" point is formed near the Wehneltzylinders of which is shown with a lying tube to the focusing onto the photosensitive layer. The magnetic beam deflection system consists of saddle coils similar to CRTs. Due to the distraction creates a focus error of the beam that must be corrected. A located in front of the photosensitive layer network ensures that the beam is not deflected by the Transhipped layer.

Developments

Philips has developed 1962 Plumbicon which lead oxide ( PbO ) was used. Advantages of Plumbicon are the compact design, ease of operation and the ability to follow a fast image change almost inertia, so this tube was used almost exclusively in TV mode and other types repressed.

Color images

Color images are made ​​possible by the use of three tubes in a camera. With a beam splitter, the incident light is divided into three tubes. Before each tube depending sits a RGB color filter of red, green and blue, so that each video tube only the corresponding color components of the image colors are recorded, which are then assembled in the subsequent display on the TV again.

For the consumer sector, this structure was too complex, there have therefore been developed cameras with filter strips. In addition to a low resolution (typically 220 columns horizontally ) showed such images taken strong moire effects.

Through the further development of the color filter mosaic filter technology used today that mitigate the moiré effect, but can not prevent it.

Size specification

A peculiarity in the size specification of the video tube determined today the sizes for sensors of digital cameras: In the past they gave the glass outer diameter of the light-sensitive front surface in inches. The real usable screen size was about 2 /3 of it. For example, the classic 1-inch vidicon XQ -1030 has an aspect ratio of 4:3 at a usable image area of ​​approximately 10 mm × 13 mm, which corresponds to a diagonal of 16.4 mm. Although one inch ( 1 ") corresponds to 25.4 mm, a tube is called a 1-inch tube that has an effective screen size of 16.4 mm. This peculiar calculation is still used today. So a modern 1/2 0.7 -inch sensor has only one real screen size of 1/2, 7 x 16.4 mm = 6.07 mm and 9.41 mm not. Depending on the sensor type and aspect ratio, the size differences vary slightly.

The calculation based on 16.4 mm ≘ 1 "can only serve as a reference value, since the ratio of tube diameter to the screen size is not a constant.